[builder] Rewrite replace paths to be absolute in generated go.mod

[milas]

Description

Convert all relative paths to be absolute for replace directives the same way that is done for modules/components.

This ensures that the output_path isn't tied to the location of the builder YAML config.

For example:

/
├── work
│   ├── mycollector
│   │   └── builder.yaml
│   ├── mylib
│   │   └── go.mod
└── dist
    └── my-collector

OCB YAML - /work/mycollector/builder.yaml

replaces:
 - registry.test/somemodule => ../mylib

Build

cd /work/mycollector
DIST_OUTPUT_PATH=/dist ocb --config ./builder.yaml

Before these changes

• Generated go.mod's replace would end up resolving to /mylib

After these changes

• Generated go.mod's replace resolves to /work/mylib

Link to tracking issue

n/a

Testing

Added unit test

Documentation

Copious comments in code, nothing user-facing

[codecov]

Codecov Report

Attention: Patch coverage is 58.53659% with 17 lines in your changes missing coverage. Please review.

Project coverage is 91.61%. Comparing base (0e9e259) to head (5875a50).

Files with missing lines	Patch %	Lines
cmd/builder/internal/builder/config.go	58.53%	12 Missing and 5 partials ⚠️

❌ Your patch check has failed because the patch coverage (58.53%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12638      +/-   ##
==========================================
- Coverage   91.66%   91.61%   -0.05%     
==========================================
  Files         478      478              
  Lines       26456    26491      +35     
==========================================
+ Hits        24250    24271      +21     
- Misses       1747     1757      +10     
- Partials      459      463       +4     

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